1. Technical Field
The invention relates generally to semiconductor chip design, and more specifically, to a power distribution method for chip-on-chip packaging of semiconductor chips containing very large scale integrated circuit (VLSI) circuits, such as microprocessors and associated memory.
2. Related Art
Chip-on-chip module technology has facilitated increased system density and increased operating frequency by reducing interconnection distances and increasing signal propagation speed. However, these advances, and increased density of the integrated circuits on the chips themselves, have generally increased power consumption and heat generation per unit volume of packaging. Thus heat-dissipation can be problem or design limitation in chip-on-chip modules, especially those containing very large scale integrated (VLSI) circuits.
Multi-chip packages are becoming more widely used in the semiconductor industry owing to the need to achieve higher performance, lower power dissipation, and lower chip fabrication and packaging costs. Dual-chip stack packages using Controlled Collapse Chip Connection (C4) interconnects (DCSC4), such as the package depicted in FIG. 1A, provide a way to provide thousands of chip-chip interconnects while also providing sufficient cooling for a less-than 10 W stack, at a relatively low cost.
FIG. 1A is a cross-sectional view of a chip-on-chip package 1 (e.g., a Dual Chip Stack package using C4 interconnections (DCSC4) package) of the related art. The chip-on-chip package 1 includes a chip-on-chip module 10 of the related art, as disclosed in FIG. 5 of commonly assigned U.S. Pat. No. 5,977,640 entitled Highly Integrated Chip-on-Chip Packaging, issued to Bertin, et al., and assigned to International Business Machines Corporation. Incorporated herein by reference are: commonly assigned U.S. Pat. No. 5,977,640; U.S. Ser. No. 09/105,382 entitled xe2x80x9cMicro-flex Technology in Semiconductor Packagesxe2x80x9d, by Bertin et al; and U.S. Pat. No. 6,225,699 entitled xe2x80x9cChip-on-Chip Interconnections of Varied Characteristicsxe2x80x9d, by Ference et al.
The chip-on-chip module 10 comprises a master chip 30 and a slave chip 40. The master chip 30 has an active side 31 and a backside 32. The slave chip 40 has an active side 41 and a backside 42. Wirebonds 28 are connected to pads 35 on active side 31 of the master chip 30, and are connected to top side 73 of a package substrate 72. The bottom side 74 of package substrate 72 is coupled to solder balls 76 for connecting the chip-on-chip package 1 to a structure or device (e.g., to a different level of packaging). Adhesive 71 between the backside 32 of master chip 30 and the top side 73 of package substrate 72 mechanically connects chip-on-chip module 10 to package substrate 72. A resin dam 66 and encapsulant 64 protect the chips (i.e., master chip 30 and slave chip 40) and impart a durability to the wirebonds 28 and chip-on-chip package 1. Metal lid 62 enables the chip-on-chip package 1 to be compact, durable, and thermally-enhanced. Metal lid 62 can operate as a heat spreader that dissipates heat released from the chip-on-chip module 10. The adhesive 71, as well as any adhesive between the metal lid 62 and the backside 42 of the slave chip 40, may have a dielectric composition.
FIG. 1B is a cross-sectional view of the chip-on-chip module 10 of FIG. 1A (shown without encapsulant 64). The chip-on-chip module 10 comprises master chip 30 and slave chip 40, fabricated in accordance with the related art. The (smaller) slave chip 40 is shown as fabricated in silicon-on-insulator (SOI) technology bonded (face to face) to the (larger) master chip 30 fabricated in bulk CMOS technology, wherein the external GND and VDD supply connections of the chip-on-chip module 10 (via wirebonds 27 and 29) are at the edge regions of the larger (master) chip 30. In the bulk CMOS technology (e.g., as on master chip 30), transistors are formed directly on the active surface 34 of a bulk semiconductor substrate (e.g., bulk semiconductor substrate 33). In the case of a SOI chip (e.g., slave chip 40), transistors are formed in a semiconductor layer 43 of semiconductor material (e.g., silicon) that is formed on an insulation layer 46 (e.g., SiOX or Al2O3) that is formed on a bulk semiconductor substrate 48 (e.g., silicon). In SOI chips of the related art, a substrate contact may be provided through the insulation layer 46 to conduct electrons between the bulk semiconductor substrate 48 and the semiconductor layer 43, and/or between the bulk semiconductor substrate 48 and one power plane for the purpose of preventing electrostatic charge from accumulating on either side of the insulation layer 46 in such a manner as to interfere with the operation of the device 47.
A portion of the electric power current (I) required to power the Chip-on-chip module 10 is delivered to the smaller chip (i.e., slave chip 40) for operation of devices (e.g. CMOS transistors, inverters, etc.) on the active side 41 of the smaller chip (i.e., slave chip 40). All the electric power current (I) is delivered to the devices 37 and 47 (e.g., semiconductor devices, indenters) on the chips in the conventional manner, e.g., through power planes (e.g., 54, 55, 56, 57) formed in metalization layers in the back-end-of-line (BEOL) layers; e.g., BEOL layers 59 and 52 of the master chip 30 and slave chip 40, respectively. For example, current ids provided to device 47 on the active side 41 of the smaller chip (i.e., the slave chip 40) is delivered at supply voltage VDD through wire 29 to the edge of the larger chip (i.e., the master chip 30) and though the VDD power plane 54 in the BEOL layer 59 of the master chip 30, through interconnections 50 (e.g., one or more solder balls) connecting master chip 30 to slave chip 40, then through the VDD power plane 56 in the BEOL layer 52 of the smaller chip (i.e., the slave chip 40), through the devices (e.g., device 47 such as an inverter) of the smaller chip (i.e., the slave chip 40), and out through the Ground (GND) power plane 57 in the BEOL layer 52 of the smaller chip (i.e., the slave chip 40), then through the interconnections 50 (e.g., solder balls) between the master chip 30 and the slave chip 40, then through the ground (GND) power plane 55 in the BEOL layer 59 of the master chip 30, and then through the ground wire 27.
Note that the VDD power planes 54 and 56, and GND power planes 55 and 57, especially in the slave chip 40, are compromised by the impedance (e.g., resistance) to the portion of current that must flow through interconnections 50 (e.g., a series of C4 connections) and wires 29 as well as through the power planes of master chip 30. Persons skilled in the art will recognize that the power planes of the master chip 30 are not as well-connected to devices (e.g., device 37) on the active surface 34 of master chip 30 in chip-on-chip module 10 as a single C4 chip in a ceramic single-chip package would be, because the interconnections 50 to the slave chip 40 prevents access points into and prevents power plane continuity in the center region of the master chip 30.
Advances in microprocessor chip technology have resulted in semiconductor chips comprising over a hundred million transistors running at frequencies greater than 1 Ghz, and have intense RAM memory bandwidth requirements. Two very high performance chips, such as chips containing a microprocessor and memory, can together consume power and release that energy as heat on the order of 100 watts, which can exceed the power-distribution and heat-dissipation capacity of DCSC4 designs of the related art. Future applications for compact modules, such as processors, workstations, graphics engines, speech recognition systems, network-connected game consoles, etc. will require extremely high bandwidth connections between a processor chip and a memory chip and may consume well over 100 W of power. The DCSC4 module shown in FIG. 1B is inadequate to provide a stable, low-impedance power supply to VLSI chips for these applications, and may not provide enough cooling for such a component. The problems of delivering sufficient useable electric power in, and getting all the heat byproduct out, are problems that must be solved before the advantages of DCSC4 packaging can be fully exploited for these high power applications.
In the vast majority of chip designs today, the power planes are basically two wiring mesh networks constructed within the back-end-of line (BEOL) metalization/wiring levels of each chip. These wiring mesh networks provide the ground (GND) connection and power supply voltage (VDD) to all of the devices (e.g. transistors) and circuits on the active side (e.g., 31 and 41) of each chip. For a chip (e.g., master chip 30) that is wirebonded to a package substrate (e.g., package substrate 72), these power planes can be connected to a relatively small number of redundant wire bond pads (e.g., pads 35 in FIG. 1A) on the active side 31 of the master chip 30, which after packaging may be connected to one or several external conductors of the package.
In higher performance, higher power chip designs, the resistance of the power supply planes in wirebond packages can result in so much xe2x80x9cbouncexe2x80x9d that circuits fail to operate properly. This a prime reason for designs moving into C4 packages, where, in general, many more power supply connections are available between the substrate and the chip, and which are distributed more evenly over the chip surface, thus creating lower power supply impedance. However, as extremely high performance chip groupings (e.g., microprocessor-memory modules) move to DCSC4 packages, the availability of a low-impedance power supply once again becomes a problem, since all connections external to the chip-on-chip package 1 must now come from the peripheral edges of the master chip 30.
Accordingly, there exists a need in the industry for a chip power distribution design capable of solving the above-mentioned problems.
A first aspect of the present invention provides a chip-on-chip module structure, comprising:
a first semiconductor chip comprising a first wiring layer on a first side of the first semiconductor chip and a first electrically conductive substrate on a second side of the first semiconductor chip, wherein the second side of the first semiconductor chip is adapted to be electrically coupled to a supply voltage VDD; and
a second semiconductor chip comprising a second wiring layer on a first side of the second semiconductor chip and a second electrically conductive substrate on a second side of the second semiconductor chip, wherein the second side of the second semiconductor chip is adapted to be electrically coupled to a ground voltage GND, wherein the first side of the first semiconductor chip is electrically coupled to the first side of the second semiconductor chip, and wherein the first semiconductor chip and the second semiconductor chip are adapted to receive power from the supply voltage VDD and the ground voltage GND.
A second aspect of the present invention provides a method for forming a chip-on-chip module structure, comprising:
providing a first semiconductor chip, said first semiconductor chip comprising a first wiring layer on a first side of the first semiconductor chip and a first electrically conductive substrate on a second side of the first semiconductor chip, wherein the second side of the first semiconductor chip is adapted to be electrically coupled to a supply voltage VDD;
providing a second semiconductor chip, said second semiconductor chip comprising a second wiring layer on a first side of the second semiconductor chip and a second electrically conductive substrate on a second side of the second semiconductor chip, wherein the second side of the second semiconductor chip is adapted to be electrically coupled to a ground voltage GND; and
electrically coupling the first side of the first semiconductor chip to the first side of the second semiconductor chip, wherein the first semiconductor chip and the second semiconductor chip are adapted to receive power from the supply voltage VDD and the ground voltage GND.
The chip-on-chip module of the present invention overcomes limitations of the related art. For example, the present invention improves interconnection density, increases the rate of heat dissipation, reduces electrical power consumption, and facilitates a more efficient delivery of electrical power into the chip-on-chip module.